They will hit the ground if you pull the stick back before they are up to proper rpm.
Get some proper training before you attempt to spin the blades.
I had 25’ hughes blades on my B8m and the length was not a problem.
There were several versions of the Bensen offset gimbal rotor head. Over the years, Bensen re-designed them stronger and stronger. The later models ought to be fine; the earlier ones, maybe not so much.
There were several versions of the Bensen offset gimbal rotor head. Over the years, Bensen re-designed them stronger and stronger. The later models ought to be fine; the earlier ones, maybe not so much.